Medium Access Control Protocol In Ad Hoc Networks With Single Shared Channel

Ad Hoc Network is a multi-hop and self-organized wireless network. In such networks, Medium Access Control (MAC) protocol plays a pivotal role in Ad Hoc network performance, for its direct determination of many properties of the shared wireless channel accessible by senders and receivers.As properties like multi-hop routing, dynamic topology, time-varying wireless interference and distributed coordination are considered, this dissertation focuses on the performance of MAC, by analyzing essential problems that cause performance degradation, and by proposing and evaluating related solutions to such problems. My thesis has the following main contributions:(I). Multi-rate is supported by most current MAC protocols, and is regarded as an effective method for choosing a proper rate according to current wireless channel conditions. However, current rate-adaptation solutions are suboptimal due to no method to qualitatively adjust the rate according to current channel state, or too complex for portable wireless terminals. A rate-adaptation scheme is proposed, which can optimize the goodput by quantitatively choosing the rate and packet length. The scheme employs two mechanisms: BER-Probing-based SNR Estimating (BPSE) and SNR-estimating-based Length and Rate Adaptation (SLRA). During the BPSE process, a high-speed special mode frame is sent, bit error rate (BER) is fed back to the sender, as well as signal to noise (SNR) and BERs for each rate are obtained by looking up the empirical BER/SNR curve. During the SLRA process, the equation of goodput relative to BER and frame length is solved, to obtain the maximized goodput and its related BER and frame length. To simplify the complex calculation above for portable wireless terminals, a proximate calculation is proposed that uses table lookup based mechanism. Theoretical analysis and simulation results show that, the maximum goodput is achievable by choosing proper values for the rate and frame length.(II).Conventional MAC protocols adapt some fixed low-speed request to send (RTS)/clear to send (CTS) handshaking mechanism. However it is not suitable for multi-and high-speed Ad Hoc networks for the incurrence of serious over-interference area and poor performance in such environment. A scheme is proposed to solve this problem, which includes Adaptive-RTS (A-RTS) and Adaptive-CTS (A-CTS) at both sender and receiver side. At the sender side, when a RTS retransmission time-out occurs, A-RTS will decrease to...